Just switched to iPhone from MotoQ and have a HF850 in my 2006 Toyota Avalon.
I was told by AT&T when purchasing the iPhone the HF850 was not supported at all. This is partially true.
Here is how to make your HF850 work with your iPhone.
1. Pair your HF850 with the iPhone in settings(enter passcode: usually "0000"). Make sure your HF850 is in pairing mode.
2. Make sure your HF850 center blue button is on indicating a bluetooth connection.
3. Press the green "voice dial" button and hold for a second
4. Your stereo will cut out if on and you should hear the light hiss of blue tooth in your car's speakers.
5. Initiate a phone call from your iPhone
6. The iPhone will disconnect from HF850 when call is terminated
Just keep in mind you must press the voice-dial button to get the HF850 to pair.
Not perfect, but better than no car kit!